Astable multivibrator d.c. bell

ABSTRACT

A direct current bell is provided having a reciprocating bell striker driven by an astable multivibrator having first and second timing capacitors of different values for providing a 40 percent duty cycle at the natural frequency of the bell striker. A means is provided for protecting the transistors of the multivibrator from excessive reverse bias potentials generated by the timing capacitors.

United States Patent 11 1 ASTABLE MULTIVlBRATOR Berns Dec. 25, 1973 [54] ASTABLE MULTIVIBRATOR D.C. BELL 3,188,623 6/1965 Culbertson 317 146 3,249,933 5/1966 McKee [75] Inventor Charles Ber, Brookfield Conn- 3,147,408 9 1964 Yamamoto et al. 317 146 73 A i Edwards Company, Inc" Norwalk 2,981,898 4/1961 St. John 317/146 C0nn 3,202,904 8/1965 Madland 321/45 R [22] Filed: Apr. 14, 1972 Primary Examiner-John W. Caldwell PP N04 244,312 Assistant Examiner-Marshall M. Curtis Regated Application Data Att0meyHarold S. Wynn et al. [63] Continuation of Ser. No. 53,752, July 10, 1970,

abandoned.

[57] ABSTRACT [52] US. Cl 340/396, 307/265, 3313710114464 A direct Current be is provided having a reciproczm [51] Int Cl G1 0k U065 ing bell striker driven by an astable multivibrator hav- Fie'ld E 392 396 ing first and second timing capacitors of different valf ues for providing a 40 percent duty cycle at the natu- 340/400-403 317/146 321/ 6 23 ral frequency of the bell striker. A means is provided for protecting the transistors of the multivibrator from 5 6] References Cited excessive reverse bias potentials generated by the timin ca acitors. UNITED STATES PATENTS g p 2,360,666 10/1944 Fish 340/392 3 Claims, 2 Drawing Figures R 3 R 1 R2 R 4 R5 l D3 C2 D2 OUTPUT PATENTEUnmzs ma :5 '6 2| 7N Ila-"$3 l4 (A :(n a 20 Liv l9 {:1 h

I mx Q kx' L\ l7 III/IA FIG. 1

R3 R| R2 R4 7\IL DI C ASTABLE MULTIVIBRATOR FIG. 2

OUTPUT ASTABIJE MULTHVIBRATOR D.C. BELL This is a continuation of application Ser. No. 53,752 filed July 10, I970 now abandoned.

BACKGROUND OF INVENTION This invention relates to noise making apparatus and in particular to a direct current actuated bell mechanism.

Generally, in order to operate a vibratory mechanism, such as a bell striker or buzzer by means of a direct current, it is necessary to provide an interrupt tothe input current for periodically deenergizing the striker assembly. Usually this interrupt takes the form of a set of contact breaker points completing a circuit to a driver mechanism which actuates the striker and which is controlled by the motion of the striker. As the striker is drawn towards the bell or gong, the contacts are opened for deenergizing the actuating circuit and releasing the striker.

The presence of a contact mechanism, however, presents certain difficulties. The most apparent of which is that the contacts eventually become worn andmust be replaced. Another and probably more important consideration is that of the safety. When the bell striker mechanism is actuated and the contacts are suddenly open, generally an arcing occurs across the contact points which in certain locations may be particularly hazardous as for example a hospital, a laboratory or a factory where the possibility of a sudden and violent fire may be present.

In addition to the problems of wear and safety, there is also a consideration relative to the construction of this type of mechanism. Economy of manufacture and ease of assembly are attributes of this type of mechanism which has not heretofore been completely satisfactory.

Anothe problem which might arise in this type of device results from overheating of the driving means. Generally, the driving means in a bell striking apparatus is an electrically operated solenoid which is initially energized through an actuating switch and the contact breaker points and is deenergized by the opening of the contacts as the bell striker travels towards the gong. The solenoid operating the bell striker is generally energized for a substantial portion of the period of operation of the bell striker and as such has a tendency to overheat and thus deteriorate the life of the apparatus. Obviously the interrupter contacts of a conventional bell mechanism are quite economical and therefore replacing the interrupter contacts with an electronic circuit places the electronic circuit at a severe economic disadvantage. The present circuit is designed to use economical electrical components to reduce the economic disadvantage.

It is therefore an object of the present invention to provide an arrangement which substantially obviates one or more of the limitations and disadvantages of the described prior arrangement.

It is another object of the present invention vide a simplified bell striker mechanism.

It is yet another object of the present invention to provide a more durable operating mechanism.

It is a more specific object of the present invention to provide an electronic circuit which obviates the need for interrupter contacts.

It isanother object of the invention to provide an electronic circuit using components which, standing to proalone, would be damaged by the potential to which they might be exposed.

SUMMARY OF INVENTION There has been provided a bell mechanism actuated by a. direct current signal including a housing, a gong mounted to the housing and a solenoid actuated striker assembly for ringing the gong. The improvement for actuating the solenoid comprises an electronic driver which periodically actuates the solenoid in lieu of contact points and includes an asymmetric freerunning multivibrator adapted for energizing the solenoid for approximately 40 percent of the duty cycle of the multivibrator for minimizing heat generation in the solenoid. For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, while its scope will be pointed out in the appended claims.

BRIEF DESCRIPTION OF DRAWINGS FIG. l is a partial broken away view showing the bell and striker assembly.

FIG. 2 is a schematic diagram of the electronic circuit governing the striker assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the bell 10 which includes a base 11, a gong l2 suitably mounted to the base 11, and a striker assembly including a striker rod 14 actuated by a solenoid 15. The solenoid 15 is mounted in a bracket 16 which is held or secured to the base 11 by adjustable plate 17. The striker rod I4 engages with the gong 12 through the aperture 13. Slots 18 are provided so that the position of the plate 17 may be adjusted in accordance with the throw of the striker rod 14.

Input energy is provided through and terminals A, A respectively supplying energy to the components mounted on printed circuit board 20. The circuits provided on the printed circuit board 20 are used to generate a signal for energizing the solenoid 15 and driving the striker M. The printed circuit board 20 is attached to the bracket 16 by another bracket 21 which also serves as a heat sink for output transistor T3 mounted to the printed circuit board 20.

When energy is supplied to the circuit over the terminals A, A, a signal is generated in the circuits provided converting the direct current input to substantially a square wave output. The square wave periodically energizes the solenoid 15 on its positive-going pulse and draws the striker arm 14 towards the gong against a bias of spring 19. When the signal goes negative, the coil is effectively deenergized and the striker arm is released or pulled up away from the gong. The frequency of the bell is therefore dependent upon the frequency of the square wave signal.

In order to provide for a more efficient striker assembly wherein a minimum of power is consumed, the natural frequency of the striker rod 14 in cooperation with the spring 19 biasing is coordinated with that of the frequency of the electronic driver mounted on printed circuit board 20. That is, the square wave signal generated by the electronic circuit has a frequency which is substantially the same as that of the natural frequency of the striker rod assembly.

- For a better understanding of the electronic circuit in driving the solenoid 15 and striker rod 14, attention is now directed towards FlG. 2. The transistors T1 and T2 are appropriately labeled as part of a stable multivibrator circuit. As will be explained later on in the discussion, a resistor R1 has a value somewhat greater than the value of a resistor R2 in the order of while a capacitor C2 is has a value greater than the value of a capacitor C1 by a factor of about 3.

When a positive input is applied across the terminals A, A the capacitors C1, C2 are discharged and therefore a positive potential is presented at the base of transistor T1 and it turns on. With transistor T1 on, current will flow from terminal A through load resistor R3 to the collector-emitter junction to the negative terminal A. The conductance of the transistor T11 essentially draws the left hand terminal of capacitor C2 to a negative potential and initiates or provides a path for charging the capacitor C2. Capacitor C2 is charged from positive energy at terminal A through resistor R2 through C2 to the conducting transistor T1. Capacitor Cl charges from positive energy at terminal A through resistor R4 and through capacitor C1 and the base to emitter circuitof transistor T1 to terminal A. Eventually, capacitor C2 charges sufficiently to provide a positive bias on the base of transistor T2 to cause it to achieve a conductance state through the diode D2. A conductance state on the transistor T2 from terminal A through load resistor R4 through the transistor T2, collector-emitter junction to the base of output transistor T3 causing it to achieve a conductance state. The right hand terminal of Cl under these conditions is suddenly switched from a positive potential to the same potential as the terminal A. Under these conditions, the transistor T1 becomes cut off by the reverse bias initiated by the conductance state of transistor T2. A path now exists for charging capacitor C1 from terminal A through resistor R1 to capacitor C1. Again, when the capacitor C1 achieves sufficient positive voltage on its left side, it forward biases diode D1 and essentially turns on transistor T1 causing the left side of C2 to be suddenly switched from a positive potential to negative potential and reverse biasing diode D2 and subsequently shutting off transistor T2.

The time constant associated with the resistorcapacitor combination R2, C2, and R1, C1 are in a ratio of approximately 3 to l. The ON times of the transistor T1 and T2, therefore, are not equal but are in fact on for approximately 60 and 40 percent of the period of the astable multivibrator respectively. The output transistor T3, therefore, is only conducting for 40 percent of the period of the flip-flop in response to the ON time of the transistor T2.

When transistor T3 conducts, current flows from terminal A through the coil 22 of solenoid 15 causing the striker M to engage the gong 12. When the transistor T2 cuts off, the output transistor T3 is also shut off and the coil 22 discharges through the diode D3 and resistor R5. Capacitor C3 is used to protect against small transients which may be present on the input power supply.

The diodes D1 and D2 serve to protect their respective transistors T1 and T2 from an excessive reverse bias on their base electrodes. That is, as previously noted, when the transistors T1 and T2 are alternately rendered conducting, the left side of the charged ca pacitor C2 and the right side of charged capacitor C1,

respectively, are suddenly switched from a positive potential to a negative potential. Accordingly, the other sides of the capacitors are switched to a potential which is more negative than that of A. The diodes D1 and D2 protect their respective transistors from this more negative potential which would reserve bias the transistors and would damage the respective transistors if they were not protected by the diodes. That is, the diodes permit the use of more economical transistors which are not required to withstand the large negative potential on their base. I

The purpose for providing asymmetric operation of the astable multivibrator becomes apparent when it is realized that it is only necessary to momentarily energize the coil 22 of solenoid 15. That is, only sufficient energy is needed to pull the striker arm 14 to stroke a gong 12. Any energy in excess of this is essentially wasted because there is only one engagement of the striker arm 14 with the gong 12 for each ON period of the transistor T3. If energy is continually or excessively applied to the coil 22 of the solenoid 15, it must be dissipated in the coil which causes the coil 22 to become heated. The particular design of the astable multivibrator was developed in order to obviate this problem and provide only sufficient energy to actuate the striker bar 14 and quickly release it. This system, therefore, serves to increase the useful life of the bell striker apparatus by minimizing the effects of heating due to electrical over load.

The period of the astable multivibrator was also designed in accordance with the natural frequency of the bell striker 14 and spring 19 bias described in connection with FIG. 3. As would be apparent to one skilled in the art, matching the natural frequency of an electromechanical device with that of the energizing input, would produce the most efficient response from the electromechanical device. The frequency of the astable multivibrator therefore was specifically designed with this response characteristic in mind.

There has therefore been provided a bell mechanism actuated by a direct current signal having an electronic driver for actuating an electromechanical solenoid in lieu of contact points. The electronic driver includes an asymmetric free-running multivibrator adapted for energizing the solenoid for approximately 10 percent of its duty cycle for minimizing degeneration in the apparatus.

While there has been described what is at present in the preferred embodiment of the present invention, it would be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is therefore aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An astable multivibrator driven D.C. bell having a housing, a gong supported by the housing and a solenoid actuated striker assembly for striking said gong wherein the improvement comprises:

a. an asymmetric free-running multivibrator which generates a frequency comparable to the natural frequency of the striker assembly for periodically actuating said solenoid actuated striker assembly and including:

1. first and second timing means including first and second capacitors, respectively, and wherein said 6 first and second timing means have different timwhich is controlled jointly by the timing means and ing values effective when activated for controlthe first and second transistors for delivering an ling the periods of energization and deenergizoutput to the solenoid during the time interval ation, respectively, of the solenoid of said solewhen the first timing means is active, noid actuated striker assembly so that the period 5 c. whereby the solenoid is energized for less than 50 of deenergization is always greater than the pepercent of the duty cycle time for each actuation riod of energization, of the striker assembly when it is actuated at a fre- 2. first and second transistors governed by the timquency comparable to the natural frequency of the ing means for alternately activating the first and striker assembly. second timing means, 10 2. An astable multivibrator driven D.C. bell accord- 3. one terminal of said first and second capacitors ing to claim 1 wherein the driver circuit means provides of the first and second timing means being conan output for a duration that is approximately 40 pernected to the base of the first and second transiscent of the duty cycle time of the striker assembly. tors, respectively, through individual diodes and 3. An astable multivibrator driven D.C. bell accordhaving the other terminal of said first and second ing to claim 1 wherein the multivibrator and driver circapacitors connected to the collectors of the seccuit means are assembled on a printed circuit board 0nd and first transistors, respectively, and which is in turn secured within the housing by a bracket wherein said diodes are poled for protecting said which also serves as a heat sink for the driver circuit transistors against an excessive reverse bias, and means.

b. driver circuit means including a third transistor 

1. An astable multivibrator driven D.C. bell having a housing, a gong supported by the housing and a solenoid actuated striker assembly for striking said gong wherein the improvement comprises: a. an asymmetric free-running multivibrator which generates a frequency comparable to the natural frequency of the striker assembly for periodically actuating said solenoid actuated striker assembly and including:
 1. first and second timing means including first and second capacitors, respectively, and wherein said first and second timing means have different timing values effective when activated for controlling the periods of energization and deenergization, respectively, of the solenoid of said solenoid actuated striker assembly so that the period of deenergization is always greater than the period of energization,
 2. first and second transistors governed by the timing means for alternately activating the first and second timing means,
 3. one terminal of said first and second capacitors of the first and second timing means being connected to the base of the first and second transistors, respectively, through individual diodes and having the other terminal of said first and second capacitors connected to the collectors of the second and first transistors, respectively, and wherein said diodes are poled for protecting said transistors against an excessive reverse bias, and b. driver circuit means including a third transistor which is controlled jointly by the timing means and the first and second transistors for delivering an output to the solenoid during the time interval when the first timing means is active, c. whereby the solenoid is energized for less than 50 percent of the duty cycle time for each actuation of the striker assembly when it is actuated at a frequency comparable to the natural frequeNcy of the striker assembly.
 2. first and second transistors governed by the timing means for alternately activating the first and second timing means,
 2. An astable multivibrator driven D.C. bell according to claim 1 wherein the driver circuit means provides an output for a duration that is approximately 40 percent of the duty cycle time of the striker assembly.
 3. An astable multivibrator driven D.C. bell according to claim 1 wherein the multivibrator and driver circuit means are assembled on a printed circuit board which is in turn secured within the housing by a bracket which also serves as a heat sink for the driver circuit means.
 3. one terminal of said first and second capacitors of the first and second timing means being connected to the base of the first and second transistors, respectively, through individual diodes and having the other terminal of said first and second capacitors connected to the collectors of the second and first transistors, respectively, and wherein said diodes are poled for protecting said transistors against an excessive reverse bias, and b. driver circuit means including a third transistor which is controlled jointly by the timing means and the first and second transistors for delivering an output to the solenoid during the time interval when the first timing means is active, c. whereby the solenoid is energized for less than 50 percent of the duty cycle time for each actuation of the striker assembly when it is actuated at a frequency comparable to the natural frequeNcy of the striker assembly. 